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Topic: ColorChecker passport, what's wrong? (Read 28635 times)

Hi guys, simple question. Why is it that it is only my flash-color profile that gives me the correct reds?Every ambient-profile, dual-illuminant or single, outdoor/indoor, sun/shade everything, the sampled wb and the CC-shot gives me reds that are WAY off and purple. All people's lips looks blueish, and red sweaters looks purple. See example:

CORRECT COLORS (flash): I understand it's very hard for you guys to see if it's right colors or not, not having the subjects in front of you, but this one is highly accurate.

WRONG COLORS (overcast): Here you can see the reds turns to some nasty purple. I've tried this a thousand times, same results. I was quite surprised to see the flash profile work last night.

And to me at least, the wb of the right shot is a bit warm, and I've seen that several times, that the greycard built into the CC passport gives to warm wb (why?) but that doesn't explain the purples, correcting the wb makes it even more purple.

I've never had this issue with my Ds3 and 1D3 nor with the 1DsII before it...and I shoot a lot of product with reds, both high and low key and everything in between. I have had some issues before the passport with a regular colorchecker, but only when the light I was illuminating the calibration shots had an excess of a certain wavelength. That includes late afternoon sun (more reds) and cloudy days (more cyans).

I've never had this issue with my Ds3 and 1D3 nor with the 1DsII before it...and I shoot a lot of product with reds, both high and low key and everything in between. I have had some issues before the passport with a regular colorchecker, but only when the light I was illuminating the calibration shots had an excess of a certain wavelength. That includes late afternoon sun (more reds) and cloudy days (more cyans).

When I calibrate using studio lights, there is never an issue...

i have to add i noticed this on outside shoots.

but well.. i bought it not for the easy stuff, i bought it to get correct colors under difficult conditions.

I've never had this issue with my Ds3 and 1D3 nor with the 1DsII before it...and I shoot a lot of product with reds, both high and low key and everything in between. I have had some issues before the passport with a regular colorchecker, but only when the light I was illuminating the calibration shots had an excess of a certain wavelength. That includes late afternoon sun (more reds) and cloudy days (more cyans).

When I calibrate using studio lights, there is never an issue...

i have to add i noticed this on outside shoots.

but well.. i bought it not for the easy stuff, i bought it to get correct colors under difficult conditions.

I tried underexposing the image to see what happens to the red, and then boosting saturation it really comes out great. I think the purple/pink issue, at least to a pretty big extent, is that the reds are overexposed. I got the idea from when I overexposed a shot with my iPhone and the red turned bright pink.

So what does that mean, I can't really underexpose just the reds, and why isn't the CC correct any way? All my wb-samples and the CC-shots are done with a lightmeter.

At a guess (I don't claim any specialist knowledge here) I think you have to be pretty accurate on your exposure when shooting the colour chart - if any of the patches are blown out in any of the channels the resulting colour profile won't be 100% accurate. Maybe better to underexpose slightly when shooting the chart than to overexpose? I usually bracket my shots and then choose the best exposure to create the profile from.

Edit: as an afterthought, how old is your passport? They do recommend replacing every two years to maintain accuracy.

At a guess (I don't claim any specialist knowledge here) I think you have to be pretty accurate on your exposure when shooting the colour chart - if any of the patches are blown out in any of the channels the resulting colour profile won't be 100% accurate. Maybe better to underexpose slightly when shooting the chart than to overexpose? I usually bracket my shots and then choose the best exposure to create the profile from.

I really thought an external lightmeter would get the exposure perfect. Although I have seen that the CC gets exposed differently under different light even if I use the meter, not sure why.

But the patch with red, purple pink etc are very far from being blown (the others also). I also use low iso settings to avoid color contamination.

First, the Passport is an excellent small and portable chart for field use.

But the DNG profiling software simultaneously sucks and blows, and that's not a compliment.

The first half of the problem is the DNG profiling software's fault: it only uses the classic 24 patches when building profiles; it completely ignores those other 26 patches. Considering that those other patches include both some much-more-saturated patches that really help define the camera's response as well as a number of near-neutral patches that really help nail down where the neutral axis (and therefore white balance) lies, that omission is both incomprehensible and inexcusable.

The second half is Adobe's fault, and that's the incoherent mess that is the DNG color "profiling" process. It's not even remotely theoretically possible to get anything vaguely resembling colorimetric accuracy from DNG profiles, though you can fake it by manually tweaking a DNG profile to be as close as you can get it and then build an ICC profile on top of it. Basically, if your idea of "good" or "pleasing" color means no-holds-barred impressionistic interpretations of color, DNG is for you. But if you want an accurate representation of color, DNG is a cruel and unusual tool for extraordinary rendition.

If you care about accurate color, you simply cannot use Adobe products to develop your raw files. Nor can you use many of the other popular raw development engines, such as Canon's DPP, because they suffer from the same root problem: the programmers have decided that their taste in color palettes is best for you. Accurate color, hell -- you can't even stop any of these raw developers from applying a contrast-boosting (and detail-obliterating) S-curve!

It's a real shame, too, because the hardware itself is quite readily capable of superbly accurate color reproduction. There's no reason why accurate color shouldn't be the default starting position, always available as an option, with the various "secret sauce" recipes only optionally added on top.

So what you're left with is mostly tools that come from the Free / Open Source software crowd, some of which produce superlative results but none of which have user interfaces with the spit-n-polish that Adobe products have. That is, you can use Adobe (etc.) products which are beautiful to look at but which mangle your own images, or you can use other tools that are ugly to look at but which make your own images shine.

If you go that route, you'll want something which is at least loosely based on dcraw for its development engine. My own runaway favorite is Raw Photo Processor, but there are other good options.

And your basic workflow would be to first create high quality quasi-generic ICC profiles in carefully controlled situations. The ColorChecker Passport, as useful as it is in the field, really doesn't have enough patches for that kind of work. There are other charts available for purchase that are usable, but I personally made my own chart; it has a replica of the classic 24 ColorChecker patches, another couple dozen paints, a black trap, some PTFE thread tape, a dozen or so wood chips, and a couple hundred patches printed on an iPF8100. I have some plans for a second version, but it's served me well.

Of course, you'll need a spectrophotometer to build the necessary reference files for any chart; there's enough batch-to-batch variation with any manufacturing process that you'll want to measure your actual chart, even if you buy it from a reputable source. The i1 Pro is an excellent tool for this purpose.

You'll also need software that lets you build these kinds of profiles. X-Rite doesn't include that with the software they bundle with their consumer-level instruments, but they do sell some very good and very expensive software that would work. However, if you're not afraid of the command line, ArgyllCMS produces absolutely amazing results, is free, and is superbly supported by the author on a mailing list.

So, you'd build profiles for each camera with the light sources you most care about; one for each of the camera's pre-canned white balance settings is a pretty good idea. And you might even want to consider building one such profile for each lens, as different lenses have different color characteristics.

Then, when you're shooting, you'd include a shot of the Passport as usual. When you get back to the studio, you'd do a linear gamma UNIWB development of that shot -- basically, just dump the raw file completely unmodified to a TIFF. You'd build a matrix profile from that and do a reverse lookup of D50 white, which will tell you what per-channel multipliers you need both for white balance and to normalize exposure. You'd then use those figures when developing the real shots and apply your most-appropriate custom-built pre-canned ICC profile.

That'll get you as close to perfect color as you're going to get with a DSLR. And, indeed, said color is good enough that, if you've got a similar workflow at the printing end of things, you can make copies of artwork such that the artist herself has to stare a long time at the original and copy side-by-side to be able to spot the differences -- the gamuts of the original and your printer permitting, of course.

One other note...you're having problems with reds and you're mentioning problems with overexposure. Some cameras, especially older ones, are notorious for overexposing reds, especially reds rich in infrared such as flower petals in sunlight. It's impossible to recover an overexposed image, no matter how good your profiling software.

What you can do, however, is underexpose the image sufficiently to prevent the reds from blowing, and still use the Passport to determine how to normalize the white balance and exposure in post. You're essentially applying digital ISO boost in post-production at that point so you have to be careful of noise, but you can boost a 5DIII ISO 100 exposure by a half-dozen stops in post if you're careful so it's not as much of a concern as it used to be.

I have been using the Color Checker when photographing a Persian Rug Collectors rugs and tapestries and color accuracy is very important.I used Strobes for the Passport Profile so my lighting was a known, as opposed to a variable source.I carefully check the exposure with the white Patch and make sure first it is not Clipping in Camera Raw, then I check to see that the White Patch's RGB value does not exceed around 240.These rugs ar full of Reds Purples and Blues and I have never experienced the problem you describe.Your meter is a starting point and the resulting exposure values should be check for clipping in your converter of choice, and the RGB values at a point below full 255 White.Give that a try and see what you get as a result.This really isnt a Camera Profiler, but a DNG profiler and for $40 or whatever you paid...you get what you pay for. The real Camera Profiler is around $399 to do the most definitive and accurate profile for your sensor and camera.Here is one and I cant remember the name of the high end package. Google it?http://www.pictocolor.com/incamera.htm

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Canon 5D MKIII, Hasselblad, Contax, Large Format, and of course my first Camera a German Kodak Instamatic with a Schneider lens and controls!

I have similar problem with CCP. I even replace the different one, but it turns out the monitor profile is dated. The CCP software does use the monitor profile when creating the profile. How long ago has you calibrated your monitor?